Fibrous nonwoven structures are used in a wide variety of applications, including but not limited to absorbent structures. Examples of such absorbent structures include personal care absorbent articles which are used to absorb such body fluids as urine and menses. As personal care absorbent articles have advanced in design, they have become increasingly more complex both in the number of components they contain and the very specific functions that they perform. Originally most if not all of these products were quite simple in design. Typically they included some type of body side liner, a simple absorbent core composed of wood pulp fluff and a garment side backing sheet or barrier such as a layer of plastic film. Many of these products were quite bulky due to what is now known to be their ineffective structural designs. Poor functional ability was often compensated for simply by enlarging the products such as by adding more absorbent. Very little was known about each of the components, their advantages, limitations and how they interacted with one another.
Today, a major emphasis has been on the reduction in size of these products. Diapers and feminine hygiene products such as sanitary napkins are but two examples of where a reduction in thickness has been a driving force in design criteria. Feminine hygiene products such as pantiliners are, in a relative sense, new products which have been made possible by the ability to reduce the size of the overall product. In so doing, maximum utilization of each and every component has become essential in the design of these products. The present invention is directed to such endeavors.
With respect to the ability of personal care absorbent articles to manage fluid intake and storage, low density fluid intake materials such as through air bonded carded webs have shown excellent uptake and temporary reservoir functions. They lack, however, an effective retention and storage mechanism such as can be supplied by cellulose or cellulosic components such as wood pulp fibers, also referred to as fluff. There are alternatives for addressing this deficiency such as adding retention components to the intake material or layering an intake material with a retention material within a product structure.
The addition of a retention component to the structure creates a mixture of intake and retention functions and properties. While this can be an effective structure, in some instances it is desirable to separate functions to maximize performance in a personal care product. For instance, if the lofty structure is intended as a body side liner, then the addition of cellulose may increase the amount of flowback from the liner onto the user's skin. This is clearly not a desired function and therefore should be avoided.
Another alternative is to layer or ply the retention material with the fluid intake layer. This eliminates cellulose in the body side portion of the composite but creates difficulties with regard to the interface between the intake and retention portions of the composite. Failure at this interface can cause several problems in the system including lack of durability in the physical structure and failure of fluid pathways due to insufficient communication between the two layers. The layers can be held together through any number of attachment means, including adhesive bonds and thermal bonds. Thermal bonding requires a thermoplastic component in each layer. Consequently, a substrate which is made entirely from cellulose will not be thermally bondable. Adhesive bonding can be used to attach the layers, but adhesives can impede the creation of fluid pathways between the intake and retention surfaces. Mechanical bonding, such as hydroentangling or needling, can be used to create structures with the desired level of attachment between the plies and with fluid pathways. Each method of attachment has been found to give different properties to the resultant structure. The present invention focuses on the use of entangling techniques to create a composite with specific desired properties. A further understanding of the present invention can be gained by a review of the following specification, drawings and claims.